Limit container width and add border radius candy

- Fit post images on large screen's by limiting container width.
- Make post images responsive.
- Add border radius to code blocks and images, eye candy :P.

![screen shot 2014-10-29 at 14 20 24](https://cloud.githubusercontent.com/assets/3677497/4824765/114bef10-5f5e-11e4-8fcf-813d2aa7906d.png)